1. Field of the Invention
The present invention relates generally to a manufacturing method for an infrared detector, and more particularly to a method of forming a wiring pattern for signal fetching on an inner cylinder to be used in the infrared detector.
2. Description of the Related Art
An infrared sensor (photoelectric conversion element for detecting infrared radiation) constructed of a binary or ternary compound semiconductor is usually used in a cooled condition at low temperatures down to about liquid nitrogen temperature (77 K). Accordingly, in an infrared detector employing this kind of infrared sensor, an evacuated heat insulating container having a dual structure consisting of an inner cylinder and an outer cylinder is used. An infrared permeable window is provided at a part of the outer cylinder, and an infrared sensor is mounted on a wall of the inner cylinder opposed to the infrared permeable window. In operating the infrared detector having such a construction, a refrigerant such as liquid nitrogen is stored into the inner cylinder of the heat insulating container, or a Joule-Thomson type cryogenic cooling device or the like is inserted into the inner cylinder, thereby cooling the infrared sensor to a predetermined temperature.
In this kind of infrared detector, there is a case that a wiring pattern formed of a conductor is formed on the wall of the inner cylinder, and the infrared sensor is connected through the wiring pattern to an external circuit. Particularly in case of using a multiple element type infrared sensor, it is necessary to form many fine wiring patterns, so that a method of easily forming the wiring patterns is demanded.
A typical cooling type infrared detector in the prior art employs an evacuated heat insulating container having a dual structure consisting of an inner cylinder and an outer cylinder. In the heat insulating container, an infrared sensor is mounted on an end surface of the inner cylinder, and a wiring pattern for electrically connecting the infrared sensor to an external circuit is formed on the end surface and a cylindrical side surface of the inner cylinder.
According to this prior art structure, the infrared sensor is cooled to low temperatures by putting liquid nitrogen into the inner cylinder or inserting a Joule-Thomson type cooling device or the like into the inner cylinder. A constant bias current is let flow in the infrared sensor, and a change in resistance value of the multiple element type infrared sensor, which value changes with an incident intensity of infrared radiation, is fetched as a voltage signal to the external circuit, thereby displaying an infrared image on a monitor.
In the prior art infrared detector as mentioned above, the wiring pattern for connecting the infrared sensor to the external circuit need be formed on the end surface and the side surface of the inner cylinder. In general, this kind of wiring pattern is formed by first forming a metal thin film on the end surface and the side surface of the inner cylinder and then irradiating a laser beam to the inner cylinder to thereby vaporize off a part of the metal thin film. In this case, the pattern on the end surface must be continuous to the pattern on the side surface. Accordingly, position adjustment with a very high accuracy is needed between in irradiating the laser beam onto the end surface of the inner cylinder and in irradiating the laser beam onto the side surface of the inner cylinder. This position adjustment requires a troublesome work.
In the case that the irradiation of the laser beam onto the metal thin film formed on the end surface precedes the irradiation of the laser beam onto the metal thin film on the side surface, an irradiated position of the laser beam on the end surface cannot be easily acknowledged by image recognition from the side of the side surface in the step of irradiating the laser beam onto the metal thin film formed on the side surface. Accordingly, a position of irradiation of the laser beam on the side surface must be defined by numerical control or the like.